This paper analyzes the effects of power outages and constraints on manufacturing firms' revenue-based total factor productivity in developing countries. The empirical analysis is based on the World Bank Enterprise Survey datasets for 84 countries over 2006-2019. The paper starts by showing statistically that firms facing power outages differ and operate in very different environments compared to firms not facing power outages, underlining a potential nonrandom issue of the treatment variable. The matching-based approach (entropy balancing) is designed to contain this type of bias. It shows that power outages negatively and significantly affect firm-level revenue-based total factor productivity, with a 9 percent lower unconditional average productivity for exposed firms compared to nonexposed firms. Moreover, the estimates suggest a connection between the severity of self-reported power constraints or obstacles by firms and the magnitude of revenue-based total factor productivity loss. The results also indicate that the effect of power outages on firm-level revenue-based total factor productivity could be influenced by the stage of economic development (low-income countries, lower-middle-income countries, upper-middle-income countries), and the ability of firms to engage in research and development and purchase backup generators. These findings suggest that to ensure economic development, the government should provide a stable power supply that can mitigate the negative shocks faced by manufacturing firms and enhance their productivity and competitiveness, allowing them to drive economic growth.